Circuits and Ohm’s Law

Flowing Electricity, Voltage Work must be done to move a charged particle The amount of work required to move a charge between two points (the work per unit charge) is called the electric potential difference between two points The potential difference is measured in Volts (V)

Electric Circuits A Circuit is when a wire is connected to the terminals of the source to form a complete path that electrons can follow

Electrical Circuits A Circuit is a closed conducting loop through which an electric current can flow.

Electrical Circuits - Parts Source of Energy – battery, thermocouple, electric generator, photocell Resistance (load) – device that uses energy – light bulb, appliance, machine, motor Photocell - a solid-state device that converts light into electrical energy by producing a voltage, as in a photovoltaic cell, or uses light to regulate the flow of current, as in a photoconductive cell: used in automatic control systems for doors, lighting Thermocouple - a kind of thermometer consisting of two wires of different metals that are joined at both ends; one junction is at the temperature to be measured and the other is held at a fixed lower temperature; the current generated in the circuit is proportional to the temperature difference

Electrical Circuits - Parts Wires – serves as a path to conduct the electrons Switch – opens (off) and closes (on) circuit Photocell - a solid-state device that converts light into electrical energy by producing a voltage, as in a photovoltaic cell, or uses light to regulate the flow of current, as in a photoconductive cell: used in automatic control systems for doors, lighting Thermocouple - a kind of thermometer consisting of two wires of different metals that are joined at both ends; one junction is at the temperature to be measured and the other is held at a fixed lower temperature; the current generated in the circuit is proportional to the temperature difference

Circuit Diagrams Photocell - a solid-state device that converts light into electrical energy by producing a voltage, as in a photovoltaic cell, or uses light to regulate the flow of current, as in a photoconductive cell: used in automatic control systems for doors, lighting Thermocouple - a kind of thermometer consisting of two wires of different metals that are joined at both ends; one junction is at the temperature to be measured and the other is held at a fixed lower temperature; the current generated in the circuit is proportional to the temperature difference

Circuit Diagram Symbols Photocell - a solid-state device that converts light into electrical energy by producing a voltage, as in a photovoltaic cell, or uses light to regulate the flow of current, as in a photoconductive cell: used in automatic control systems for doors, lighting Thermocouple - a kind of thermometer consisting of two wires of different metals that are joined at both ends; one junction is at the temperature to be measured and the other is held at a fixed lower temperature; the current generated in the circuit is proportional to the temperature difference

Types of Electrical Circuits Series All the parts of an electric circuit are connected one after another Only 1 path for the electron to take

Series Circuit

Types of Electrical Circuits Parallel Different parts of an electric circuit on separate branches Several paths for electrons to take

Parallel Circuit

Series Circuit Disadvantage: if there is a break anywhere in the circuit, the entire circuit is open and no current can flow Ex: cheap holiday lights

Series Circuit

Parallel Circuit If there is a break in one branch, the electrons and current can still flow through the other branches Ex: more expensive holiday lights Your house is wired with parallel circuit

Parallel Circuit

Electric Current A flow of charge (electrons) is called an electric current letter variable = I (electric current) The amount of charge that passes a given point per second The unit for current is the ampere (A) or amp for short

Resistance to Flow Items in the circuit resist the flow of electrons Load/appliance, lights, TVs Wires The current is slowed by interactions with the load and atoms in the wire a property of a conductor by virtue of which the passage of current is opposed, causing electric energy to be transformed into heat:

Resistance to Flow Resistance Factors that affect resistance: Letter variable = R Unit = ohms (Ω) Factors that affect resistance: Resistance Increases with, longer wire Resistance Increases with higher temperature Resistance Decreases with a thicker wire a property of a conductor by virtue of which the passage of current is opposed, causing electric energy to be transformed into heat:

Ohm’s Law Ohm’s Law states the relationship between voltage difference, current and resistance in a circuit. Ohm’s Law states that the current in a wire (I) is equal to the voltage (V) divided by the resistance (R) I=V/R

Ohm’s Law Current (l) = amperes Voltage (V) = Volts Resistance (R) = Ohms

V R I Practice Problem 1 Calculate the voltage difference in a circuit with a resistance of 25 Ω if the current in the circuit is 0.5 A.

V R I Practice Problem 2 Find the current in a circuit that has a voltage of 120 volts and a resistance of 60 Ω.

V R I Practice Problem 3 Find the resistance of a circuit that has a voltage of 120 volts and a current of 4 amperes.